People underestimate Rancor, 100% guaranteed that no one expects the damage you put out early. Against mages if you see them cast their spells, all in them and force them back. Be aware of minimap and position accordingly, don't let your aggression cause multiple deaths to ganks.

Once you hit level 7, you turn into the best hyper carry in game. The movement speed allows for easy skillshot dodges, mixed with insane chase potential and escape mechanics. You ARE the fastest hero in the game at level 7, so make sure you use that to your advantage.

On maps such as curse, I love to stay and push a lane. Rancor Valla absolutely destroys buildings and grenades obliterate minion waves. But I do not wan't you to play the game like a robo-goblin, just take advantage of situations to get an XP lead early.

If you are confident in your skills as a ranged assassin, and don't need to take the defensive talents, you will do all the damage. But if the defensive talents are needed, it's fine you still hurt(trust me).

Frost shot mixed with executioner = the hardest hitting auto attacks in the game(aside from butcher zeratul atm). Not only will this allow you to CC the enemy and deal more damage but mixed with you movement speed, this makes for an insanely easy time kiting around.

If you are on the defensive in the game because you are behind, don't worry take what you need to survive. Then continue to do the damage, just do not position as aggressively as you normally would.